The NSW government has apologised to people who were stranded in central Sydney after thousands flocked to see the world's largest passenger ship.

Govt apologises for transport chaos

The NSW government has apologised to people who were stranded in central Sydney after thousands flocked to see the world's largest passenger cruise ship.

Traffic ground to a halt and bus, train and ferry services were overwhelmed by the crowds who gathered to see the Queen Mary 2 and its smaller sister ship, Queen Elizabeth 2.

Assistant Transport Minister Eric Roozendaal said the government had underestimated the number of people who would travel into the city to see the ships.

"Last night was a spectacular event with the QE2 and the QM2 coming to Sydney and the fireworks," he told reporters.

"Unfortunately, I know families were delayed on their way home and I am sorry for that delay.

"Clearly we did underestimate the massive response from Sydney."

Premier Morris Iemma said Cunard, which owns the two liners, had been amazed at the number of people who had flocked to Sydney Harbour.

"Plans were put in place to deal with a crowd, it's just that no one could have predicted the kind of response," Mr Iemma told reporters.

"We are unhappy that people have been inconvenienced."

Mr Roozendaal said a four car accident on the Sydney Harbour Bridge and maintenance work on the Harbour Tunnel and the Cross City Tunnel had exacerbated traffic problems.

The QM2 left Sydney on Tuesday night but the QE2 will remain moored at Circular Quay until Thursday evening.

Opposition Leader Peter Debnam said the situation had been a "disaster", and questioned why the government had failed to put in place the proper crowd management measures.

"I was simply appalled yesterday with the way the government mismanaged that," Mr Debnam told reporters.

"You only have to go back through the records to see how many large ships have come in (to Sydney Harbour) and the problems they have caused.

"The government had I don't know how many months or years' notice of that event yesterday and they completely ignored it."

The Sydney Chamber of Commerce said it was unacceptable for traffic to be forced to a halt because of a visit by two cruise liners.

"Sydney can't afford to develop the reputation of being unable to host major attractions and events due to our transport system," Chamber of Commerce chief executive and former state Liberal MP Patricia Forsythe said.